The influencing factors of sodium sulfate solution physical crystallization attack on cement mortars were investigated through analyzing the changes of macroscopical capability and microstructure of cement mortars in attack process. Results indicate that with partial soaking time increasing, more and more sulfate sodium crystals grow on cement mortars surface, and cement mortars surface is denuded gradually. Compressive and flexural strength increase first and then decrease in the deterioration process. In the attack process, porosity of cement mortars decreases first and then increases. Lots of sodium sulfate crystals accumulate in pores of cement mortars and crystallization pressure is on the rise, resulting in physical crystallization attack taking place.